For many years traditional paper greeting cards have been widely used for celebratory occasions such as birthdays, graduations, weddings, and for other commercial purposes. More recently, the market has expanded with greeting cards that attempt to capture attention by means of particular designs or devices, and to add features and functions to standard paper cards to enhance the communicative and entertainment value of social and relational greetings. Mass production of digital electronics and devices has increased availability and reduced costs, but only a limited variety of cards with electronic features have been developed: